1. Field of the Invention
This invention relates to an image reading apparatus, and more particularly to an image reading apparatus of the line scanner type wherein a solid-state image sensor such as a CCD linear array for electro-optically scanning in a main scanning direction is moved in a subscanning direction perpendicular to the main scanning direction to read an object image of a document or the like.
2. Description of the Related Art
An image reading apparatus of the line scanning type, that is, the line scanner type, wherein a reading head employing a one-dimensional photoelectric transducer element such as a CCD linear array sensor is moved relative to an object image of a document or the like to read the image is widely employed as an image data inputting apparatus of a facsimile apparatus, a computer or the like.
In an image reading apparatus of the type mentioned above, control means for establishing an accurate corresponding relationship between a reading timing of image data for one line in the main scanning direction photoelectrically converted by a reading head and an amount of the relative movement in the subscanning direction are required in order to reproduce an accurate image. As a first example of a conventional image reading apparatus wherein a positioning line code which is fixed relative to the image and moves relative to the reading head is provided as the control means and the line code is read by the reading head to detect the amount of movement, an image reading/recording apparatus is disclosed in Japanese Patent Laid-Open No. 233974/85.
Referring to FIG. 1(A) which shows the first example of a conventional image reading/recording apparatus in a block diagram and FIG. 1(B) which shows a cylinder section of FIG. 1(A) in detail, the image reading/recording apparatus includes recording cylinder 101 which rotates at a uniform speed with photosensitive member 102 wound therearound, recording head 104 which moves at a uniform speed along main scanning feed screw 105 parallel to an axis of rotation of recording cylinder 101, input apparatus 110, memory 109 for storing image data from input apparatus 110, controller 108, code cylinder 121 disposed in a coaxial and fixed relationship with cylinder 101 and having on a circumferential face thereof a line code forming a plurality of parallel lines inclined by a particular angle .phi. with respect to the direction of the axis thereof, and code reading head 122 which moves at a uniform speed of a fixed ratio to the speed of movement of recording head 104 along feed screw 124 parallel to the axis of code cylinder 121 and has sensor 152 for irradiating light beam 151 upon the line code and receiving reflected light from the line code.
The line code is formed from a single main line corresponding to a one rotation pulse which is generated in one rotation of cylinder 101 and N sublines corresponding to N pulses which are generated by N in the one rotation. Since code reading head 122 moves along feed screw in synchronism with rotation of cylinder 101 and code cylinder 121, the generation phases of the one rotation pulse and the N pulses for each one rotation of code cylinder 121 proceed gradually. Supposing the ratio between the feeding speed of recording head 104 and the feeding speed of code reading head 122 is n:1, while recording head 104 advances by distance L in the axial direction of cylinder 101 as shown in FIG. 1(C), code reading head 122 advances by L/n. Accordingly, where the direction perpendicular to recording direction Y of recording head 104 thus composed on cylinder 101 is represented by X, the relationship between angle .theta. between X and the axial direction of cylinder 101 and inclination angle .phi. of the line code with respect to the axial direction of code cylinder 121 is given by the following equation:
tan.phi.=ntan.theta. PA1 .phi.=tan.sup.-1 (ntan.theta.) PA1 a scanning section including an electro-optical conversion apparatus for electro-optically scanning, by means of a plurality of photoelectric transducer elements disposed in a linear array, an original in predetermined main scanning periods in a direction of a main scanning line along the direction of the linear array to convert an image of the original into image data signals and for moving in a subscanning direction perpendicular to the main scanning direction relative to the original, PA1 a table sheet for being placed in an overlapping relationship on the original and having a transparent original area to allow the original to be observed therethrough and a pattern area including a stripe pattern disposed in parallel to the subscanning direction along a side of the original area and formed from black and white stripes having a predetermined inclination with respect to the main scanning direction and predetermined widths, PA1 pattern signal production means for electro-optically scanning the stripe pattern in the main scanning direction to produce a pattern signal of a predetermined resolution corresponding to the stripe pattern, PA1 movement detection means for detecting, in response to the pattern signal supplied thereto, that the stripe pattern moves in the main scanning direction by a distance corresponding to relative movement of the scanning section relative to the original by a predetermined distance in the subscanning direction to produce a movement detection signal, PA1 storage control means for storing the image data signals into a buffer memory for each of the main scanning periods, and PA1 corrected data production means for producing, in response to the movement detection signal outputted from the movement detection means, corrected data corresponding to the distance of the relative movement of the scanning section in the subscanning direction from the image data signals stored in the buffer memory. PA1 a scanning section including an electro-optical conversion apparatus for electro-optically scanning, by means of a plurality of photoelectric transducer elements disposed in a linear array, an original in predetermined main scanning periods in a direction of a main scanning line along the direction of the linear array to convert an image of the original into image data signals and for moving in a subscanning direction perpendicular to the main scanning direction relative to the original, PA1 a table sheet for being placed in an overlapping relationship on the original and having a transparent original area to allow the original to be observed therethrough and a pattern area including a stripe pattern disposed in parallel to the subscanning direction along a side of the original area and formed from black and white stripes having a predetermined inclination with respect to the main scanning direction and predetermined widths, PA1 pattern signal production means for electro-optically scanning the stripe pattern in the main scanning direction to produce a pattern signal of a predetermined resolution corresponding to the stripe pattern, PA1 movement detection means for detecting, in response to the pattern signal supplied thereto, that the stripe pattern moves in the main scanning direction by a distance corresponding to relative movement of the scanning section relative to the original by a predetermined distance in the subscanning direction to produce a movement detection signal and for generating, as subscanning data, the number of those main scanning lines of the image data included in the range of the relative movement of the scanning section by the predetermined distance in the subscanning direction, and PA1 a buffer memory for storing the image data signals and the subscanning data for each of the main scanning periods. PA1 a scanning section including an electro-optical conversion apparatus for electro-optically scanning, by means of a plurality of photoelectric transducer elements disposed in a linear array, an original in predetermined main scanning periods in a direction of a main scanning line along the direction of the linear array to convert an image of the original into image data signals and for moving in a subscanning direction perpendicular to the main scanning direction relative to the original, PA1 a table sheet for being placed in an overlapping relationship on the original and having a transparent original area to allow the original to be observed therethrough and a pattern area including a first stripe pattern disposed in parallel to the subscanning direction at least on one side of the original area and formed from black and white stripes having a predetermined inclination with respect to the main scanning direction and predetermined widths and at least two second stripe patterns formed from black and white stripe patterns of predetermined widths and extending in parallel to the subscanning direction, PA1 pattern signal production means for electro-optically scanning the first and second stripe patterns in the main scanning direction to produce a pattern signal of a predetermined resolution corresponding to the first and second stripe patterns, PA1 first movement detection means for detecting, in response to the pattern signal supplied thereto, that the first stripe pattern moves in the main scanning direction by a distance corresponding to relative movement of the scanning section relative to the original by a predetermined distance in the subscanning direction to produce a first movement detection signal, PA1 second movement detection means for detecting, in response to the pattern signal supplied thereto, movement of the second stripe patterns in a direction opposite to the main scanning direction when the direction of the movement of the scanning section is deflected from the subscanning direction to produce relative movement with respect to the original by a distance greater than a predetermined distance in the main scanning direction to produce a second movement detection signal, PA1 inclination detection means for measuring, in response to the pattern signal supplied thereto, the distance between two adjacent ones of the plurality of second stripe patterns to detect an inclination of the linear array with respect to the main scanning direction to produce an inclination signal, PA1 storage control means for storing the image data signals into a buffer memory for each of the main scanning periods, and PA1 corrected image data production means for producing, in response to the first and second movement detection signals, corrected image data corresponding to the distances of relative movement in the subscanning direction and the main scanning direction from the image data signals stored in the buffer memory. PA1 a scanning section including an electro-optical conversion apparatus for electro-optically scanning, by means of a plurality of photoelectric transducer elements disposed in a linear array, an original in predetermined main scanning periods in a direction of a main scanning line along the direction of the linear array to convert an image of the original into image data signals and for moving in a subscanning direction perpendicular to the main scanning direction relative to the original, PA1 a table sheet for being placed in an overlapping relationship on the original and having a transparent original area to allow the original to be observed therethrough and a pattern area including at least one first stripe pattern formed from black and white stripes disposed in the original area and having a predetermined inclination with respect to the main scanning direction and predetermined widths and at least two second stripe patterns formed from black and white stripe patterns of predetermined widths and extending in parallel to the subscanning direction, PA1 pattern signal production means for electro-optically scanning the first and second stripe patterns in the main scanning direction to produce a pattern signal of a predetermined resolution corresponding to the first and second stripe patterns, PA1 first movement detection means for detecting, in response to the pattern signal supplied thereto, that the first stripe pattern moves in the main scanning direction by a distance corresponding to relative movement of the scanning section relative to the original by a predetermined distance in the subscanning direction to produce a first movement detection signal, PA1 second movement detection means for detecting, in response to the pattern signal supplied thereto, movement of the second stripe patterns in a direction opposite to the main scanning direction when the direction of the movement of the scanning section is deflected from the subscanning direction to produce relative movement with respect to the original by a distance greater than a predetermined distance in the main scanning direction to produce a second movement detection signal, PA1 inclination detection means for measuring, in response to the pattern signal supplied thereto, the distance between two adjacent ones of the plurality of second stripe patterns to detect an inclination of the linear array with respect to the main scanning direction to produce an inclination signal, PA1 storage control means for storing the image data signals into a buffer memory for each of the main scanning periods, and PA1 corrected image data production means for producing, in response to the first and second movement detection signals, corrected image data corresponding to the distances of relative movement in the subscanning direction and the main scanning direction from the image data signals stored in the buffer memory. PA1 a scanning section including an electro-optical conversion apparatus for electro-optically scanning, by means of a plurality of photoelectric transducer elements disposed in a linear array, an original in predetermined main scanning periods in a direction of a main scanning line along the direction of the linear array to convert an image of the original into image data signals and for moving in a subscanning direction perpendicular to the main scanning direction relative to the original, PA1 a table sheet for being placed in an overlapping relationship on the original and having a transparent original area to allow the original to be observed therethrough and a pattern area including at least two first stripe patterns formed from black and white stripes disposed in the original area and having a predetermined inclination with respect to the main scanning direction and predetermined widths and at least one second stripe pattern formed from black and white stripe patterns of predetermined widths and extending in parallel to the subscanning direction, PA1 pattern signal production means for electro-optically scanning the first and second stripe patterns in the main scanning direction to produce a pattern signal of a predetermined resolution corresponding to the first and second stripe patterns, PA1 first movement detection means for detecting, in response to the pattern signal supplied thereto, that the first stripe patterns move in the main scanning direction by a distance corresponding to relative movement of the scanning section relative to the original by a predetermined distance in the subscanning direction to produce a first movement detection signal, PA1 second movement detection means for detecting, in response to the pattern signal supplied thereto, movement of the second stripe patterns in a direction opposite to the main scanning direction when the direction of the movement of the scanning section is deflected from the subscanning direction to produce relative movement with respect to the original by a distance greater than a predetermined distance in the main scanning direction to produce a second movement detection signal, PA1 inclination detection means for measuring, in response to the pattern signal supplied thereto, the distance between of the first stripe patterns to detect an inclination of the linear array with respect to the main scanning direction to produce an inclination signal, PA1 storage control means for storing the image data signals into a buffer memory for each of the main scanning periods, and PA1 corrected image data production means for producing, in response to the first and second movement detection signals, corrected image data corresponding to the distances of relative movement in the subscanning direction and the main scanning direction from the image data signals stored in the buffer memory.
Therefore,
In response to the one rotation pulse and the N pulses obtained in this manner, controller 108 controls the speeds of rotation of recording cylinder 101 and feed screw 105 by way of motor controllers 112 and 111 and motors 103 and 106, respectively.
An image reading apparatus disclosed in Japanese Patent Publication No. 34713/91, which is a second example of a conventional image reading apparatus, includes an original table in the form of a flat plate which moves back and forth in a subscanning direction relative to an image scanning section to effect subscanning. A striped pattern having a preset inclination angle relative to a main scanning direction is provided at an end of the original table and is used to generate a reference signal for movement control in the subscanning direction.
Referring to FIG. 2 which shows an appearance of an original scanning section which is one of the principal components of the second example of the conventional image reading apparatus, the original scanning section shown includes document table 201 formed from a flat glass plate having reference mark 205 in the form of a stripe pattern formed by printing on a lower face at an end thereof and document area 202 for receiving original document 204 thereon, and a scanning section including lamp 206 for irradiating light upon original document 204 and mark 205, mirror 207, lens 208, and CCD unit 209 of the linear array type having 2,048 elements.
Referring to FIG. 3 which is a perspective view of document table 201 as viewed from an upper surface toward a lower surface of the same, reference mark 205 is a stripe pattern inclined by 45 degrees with respect to the main scanning direction. Part (128 elements) of the CCD unit is allocated to optical detection corresponding to reference mark 205. Those 192 elements on the opposite side to reference mark 205 are allocated to detection of a margin.
Referring to FIG. 4 which shows a circuit of the image scanning section in a block diagram, the image scanning section includes timing generation section 251 for generating a data clock and a scanning start signal, automatic gain control circuit 252 for amplifying data from the individual elements of CCD unit 209 to supply analog data, threshold level circuit 250 for outputting binary data corresponding to a preset threshold level for the analog data, stripe analysis circuit 254 for receiving the binary data supplied thereto, performing a stripe analysis and outputting a valid video data line signal, a valid data clock and a valid line signal, and gate circuit 253 for gating the binary data with the valid video data line signal.
In operation, reflected light from original document 204 on document table 201 and reference mark 205 is projected onto the 2,048 CCD elements of CCD unit 209 by way of mirror 207 and lens 208. In response to the data clock and the scanning start signal from timing generation circuit 251, CCD unit 209 performs sequential data reading operations beginning with the 0th CCD element and ending with the 2,047th CCD element and supplies the thus read data to automatic gain control circuit 252. Automatic gain control circuit 252 amplifies the data to supply analog data, and threshold level circuit 250 compares the analog data sequentially supplied thereto with the preset threshold level to produce binary data consisting of binary values comprising a white signal "0" equal to or higher than the threshold level and a black signal "1" lower than the threshold level. The binary data are supplied to gate circuit 253, and gate circuit 253 thus gates, in response to the valid video data line signal as described hereinafter, those 128th to the 2,047th element data of the binary data which correspond to document area 202 and the margins and outputs them to the video data line.
Meanwhile, stripe analysis circuit 254 receives, from an external control circuit (not shown) which is constituted from a microprocessor, a stripe sample-on signal indicative of whether the stripe analysis circuit is operative or inoperative and a first scanning line signal indicative of arrival of a first scanning line which is generated when an top end of a document is detected, and analyzes the 0th to 127th element data to detect whether or not document table 201 and original document 204 have moved a predetermined distance.
Referring to FIG. 3, FIGS. 5(A) and 5(B) illustrating details of reference mark 205 and the analyzing operation of stripe analysis circuit 254, respectively, mark 205 is a stripe pattern constituted from white stripes 205a and black stripes 205b and inclined by 45 degrees with respect to the main scanning direction, that is, the scanning direction of CCD unit 209, as described above, and has left side dummy area 241, detection area 242 and right side dummy area 243. Here, it is assumed that the resolution is 8 picture elements/mm in the main scanning direction and accordingly is also 8 picture elements/mm in the subscanning direction, that is, 8 picture element lines/mm. Accordingly, the size of each picture element is 1/8.times.1/8 mm. If the speed in the subscanning direction is an appropriate speed, that is, a nominal feeding speed, the distance between the picture element lines is kept at 1/8 mm. However, if the speed in the subscanning direction drops lower than the nominal feeding speed, then the distance between the picture element lines becomes smaller than 1/8 mm, and consequently, the picture element lines overlap with each other. Stripe analysis circuit 254 sets detection position DP in the form of a detection window of the one picture element size and discriminates, upon relative movement of document table 201 relative to the image scanning section in the subscanning direction, whether or not the distance between scanning lines reaches the dimension of the one picture element size, that is, 1/8 mm.
The initial position of detection position DP can be set to an arbitrary picture element position within detection area 242. Here, the initial position is set to picture element position 48 for the convenience of description.
Referring to FIG. 6 which is a processing flow chart of the second conventional example described above, subsequently to step 271 for setting of the initial position of detection position DP, it is checked at next step 272 to determine whether or not black, that is, a black picture element, is found out at detection position DP of picture element position 48. Since scanning lines L1 to L3 in FIG. 5(A) do not have a black picture element at picture element position 48, NO is outputted at step 272, and image data corresponding to scanning lines L1 to L3 are abandoned, that is, ignored and are not supplied to a buffer memory (step 273). In scanning line L4, a black picture element is detected at detection position DP and stripe detection pulse SD is produced. Here, at step 272, YES is outputted, and at step 273, current scanning line L4 is handled as a new scanning line and image data of scanning line L4 are supplied to the buffer memory. The fetching of the image data is performed by gating by gate circuit 253 with the valid video data line signal described above (step 274). If a black stripe is detected, detection position DP is shifted to next picture element position 49 (step 275).
Referring also to FIG. 5(B), the operation returns to step 272 again so that next scanning line L5 is checked similarly with picture element position 49 set as detection position DP, and since a black stripe is detected, stripe detection pulse SD is generated so that fetching of the image data and shifting of detection position SD to picture element position 50 are performed.
When similar processing is thereafter performed for next scanning line L6, since the distance between scanning lines L5 and L6 is smaller than the nominal distance of 1/8 mm due to a drop of the speed of relative movement of document table 201 relative to the image scanning section, the black stripe at detection position DP (picture element position 50) is not detected, and accordingly, no stripe detection pulse SD is produced and fetching of image data is not performed. For the same reason, fetching of image data is not performed with scanning line L7. Detection of a black stripe at detection position DP (picture element position 50) takes place successfully in scanning line L8, and fetching of image data and shifting of detection position DP to picture element position 51 are performed in response to stripe detection pulse SD.
In this manner, in the present image reading apparatus, following up the variation of the speed of relative movement of document table 201 relative to the field of view of the image scanning section, that is, CCD unit 209, image data of a scanning line whose relative distance from an adjacent line reaches the nominal distance of 1/8 mm are fetched.
Detection position DP is gradually shifted rightwardly, and when it reaches picture element position 63 at the right end of detection area 242, it is returned to picture element position 32 at the left end of detection area 242 as indicated in scanning lines Ln to Ln+2.
An image reading apparatus of the hand scanner type disclosed in Japanese Patent Laid-Open No. 61182/87, which is the third example of the conventional image reading apparatus, includes a hand scanner for reading, through a transparent sheet at a portion of which position information is recorded in the form of a bar code or some other form, an original placed on the light transmission sheet, and a processing device including detection means for detecting the position information from image information read by the hand scanner, calculation means for calculating a correction coefficient from the position information detected by the detection means, and conversion means for converting the image information using the correction coefficient obtained by the calculation means, and allows inputting of an accurate image of a large original by means of the sensor of a small size by simple operations.
Referring to FIG. 7 which shows an image reading condition of the third example in a perspective view, the image reading apparatus includes original 301 similar to that of the second example, transparent sheet 302 having position information recorded in the form of a bar code at the opposite ends thereof, hand scanner 303 having a built-in sensor for obtaining image information, and processing device 304 for processing the image information.
In operation, transparent sheet 302 is first placed onto original 301, and then, hand scanner 303 is pressed against transparent sheet 302 and scans it. Image information on original 301 and the position information on transparent sheet 302 are read by the built-in sensor of hand scanner 303 and sent to processing device 304.
Referring to FIGS. 8(A) to 8(C) illustrating the concept of the image information read by hand scanner 303, when hand scanner 303 is scanned in the direction of arrow X on original 301 and transparent sheet 302 as seen in FIG. 8(A), image information including image information portions 305 and 306 at the opposite end portions of such transparent sheet 302 as shown in FIG. 8(B) can be read. Processing device 304 detects the position information from the image information at image information portions 305 and 306. Where the position information detected from image information portions 305 and 306 is represented by P1 and P2, respectively, and the leftward and rightward distance between the positions of light transmission sheet 302 at which the position information is recorded is represented by 1, inclination angle .theta. of scanning of hand scanner 303 is given by the following equation: EQU .theta.=tan.sup.-1 (P2-P1)/1.
Processing device 304 executes this calculation to obtain angle .theta. and executes conversion scanning of inclining the image information read by the scanning by angle .theta.. As a result of this conversion scanning, even the image information inputted by such inclined scanning as seen from FIG. 8(A) or 8(B) is returned into original image information as seen from FIG. 8(C). The image information of original 301 can be read by repeating the inputting sequence several times.
In an image reading apparatus of the hand scanner type disclosed in Japanese Patent Laid-Open No. 500553/89 which is the fourth example of the conventional image reading apparatus, a transparent sheet including a position identification mark disposed on a page including a printed text or some other information is scanned so that the page may be crossed. The position identification mark is printed in different colors than that of any other information on the page across the transparent sheet while the other information on the page is printed, for example, in black. In this manner, while a position sensor which is sensitive to the color of the identification mark measures the position of the image reading apparatus relating to the page, a second sensor which is sensitive to the information color, that is, black, reads desired information from the page.
Referring to FIG. 9(A) which shows the fourth example in a block diagram, the image reading apparatus includes hand scanner 314 including line sensor 316 and optical mouse mechanism 319 for scanning a book to be read, optical character recognition unit (OCRU) 322, storage section 323 formed from a RAM, and computer 324.
Referring to FIG. 9(B) which shows a bottom portion of hand scanner 314, hand scanner 314 includes line sensor 316 formed from a CCD sensor similar to that of the second or third conventional image reading apparatus described above, optical mouse mechanism 319, and light source 321 for optical mouse mechanism 319.
Referring to FIG. 9(C) which illustrates a manner in which hand scanner 314 scans a predetermined page of book 310 through transparent sheet 318, book 310 shown includes page 311 on which text 312 of an object for reading is printed.
Transparent sheet 318 has a set of equally spaced horizontal lines, for example, of red and a set of equally spaced vertical lines, for example, of green. When hand scanner 314 crosses green and red lines, a sensor in mouse mechanism 319 senses them. The numbers of lines crossed during reading scanning are added then to measure the position of image-reading apparatus 314 with respect to transparent sheet 318. Light source 321 at the bottom portion of hand scanner 314 alternately emits red light and green light to allow mouse mechanism 19 to detect red and green lines separately from each other.
In operation, referring to FIGS. 9(A), 9(B) and 9(C), line sensor 316 senses text 312 on page 311, generates an electric signal in response to text 312 and sends out the electric signal to OCRU 322. Further, OCRU 322 receives from optical mouse mechanism 319 a signal representative of the position of hand scanner 314. OCRU 322 executes one of a large number of optical character recognition algorithms to identify characters being scanned. When OCRU 322 receives a signal representative of presence of a print at a particular point on page 311 as well as information representative of the position of the point, it makes up a bit map in storage section 322 making use of the information.
Since hand scanner 314 is an apparatus of a small size, it may possibly scan information of page 311 in a direction inclined by an angle with respect to text 312. In this instance, comparing with the case wherein hand scanner 314 is held at a correct angle at which line sensor 316 is aligned in a vertical direction with text 312, the position of the particular information of text 312 provided to an end portion of line sensor 316 is sensed in an offset condition corresponding to the inclined angle. As a result, an inaccurate bit map is stored into storage section 322 by computer 324.
In the fourth conventional image reading apparatus, hand scanner 314 may be replaced by hand scanner 314A for detecting the inclination of the hand scanner whose bottom portion is shown in FIG. 9(D). Referring to FIG. 9(D), hand scanner 314A includes, in addition to line sensor 316, optical mouse mechanism 319 and light source 321, second mouse mechanism 320 and second light source 322, and provides information representative of the inclination of hand scanner 314A to computer 324.
Mouse mechanism 319 and mouse mechanism 320 provide each, each time they cross a position identification line of transparent sheet 318, an electric pulse representative of the movement. In this manner, computer 324 traces the positions of mouse mechanisms 319 and 320 and as a result traces the holding angle of hand scanner 314A, line sensor 316 provides a signal from photoelectric transducer element representative of received light and computer 324 calculates further accurately to which position of the bit map the signal corresponds.
The conventional image reading apparatus described above are disadvantageous in that, since the resolution in reading of the original in the subscanning direction is fixed even if the speed of relative movement to the original in the subscanning direction varies, if the speed of movement is raised higher than a certain limit value, reading of the original is disabled. Further, they are disadvantageous also in that, even if the speed of movement is reduced, the picture quality in reading is not improved.
The conventional image reading apparatus are further disadvantageous in that the direction of movement in the subscanning direction is one direction and reading in the opposite direction is impossible.
Furthermore, detection means for detecting the speed of movement using a conventional stripe pattern is disadvantageous in that it is great in size and complicated and it is difficult to apply it to an image reading apparatus of a small size such as a hand scanner.
Further, the transparent sheet which is employed in the third or fourth conventional image reading apparatus of the hand scanner type and on which position information is stored employs, as the position information, a bar code or very accurate graduations, and is disadvantageous in that the accuracy in detection is low or, if it is tried to assure a high degree of detection, an expensive transparent sheet is required.